Dual detector micro-XRF cryotomography and mapping on the model organism Daphnia magna

The recent availability of a cryostream cooler at beamline L has allowed synchrotron radiation based micro-XRF analysis of frozen biological samples close to their native state. In a previous contribution, we compared the elemental distributions within a ydrated (frozen) and a fixed (dehydrated) Daphnia magna, which is a freshwater crustacean used in toxicological research as a model organism for evaluating effects of metals on the cosystem. Although hydrated samples show less dislocation of elements and/or sample contamination as compared to fixed samples, they are mainly composed of a water matrix, which is more susceptible to absorption effects of low energy X-rays. Therefore, we investigate the degree of absorption in 2D/CT micro-XRF elemental maps of Daphnia magna using a dual silicon drift detector (SDD) setup

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Synthese und Charakterisierung neuartiger, gemischter Tetrahydridoborate für die Wasserstoffspeicherung

Im Rahmen dieser Arbeit wurden neuartige, gemischte Tetrahydridoborate (Borhydride), die für die Wasserstoffspeicherung im Festkörper für die mobile Anwendung geeignet sein könnten, synthetisiert und vollständig charakterisiert. Entscheidende Materialanforderungen für die Kombination mit einer Tieftemperaturbrennstoffzelle sind die hohe Wasserstoffspeicherkapazität von min. 6 m% bei einer Wasserstoffdesorption unterhalb von 100°C. Um beide dieser Hauptkriterien zu erfüllen, wurden Li-Al- und Na-Al-Borhydrid entsprechend dem Konzept von Nakamori u.a. ausgewählt. Beide Borhydride desorbieren unterhalb von 100°C, wobei das synthetisierte Li-Al-Borhydrid aufgrund des hohen Wasserstoffgehalts (17,2 m% H2) die vielversprechendsten Eigenschaften zeigte. Beide Systeme wurden mittels Pulverdiffraktometrie am Synchrotron hinsichtlich Ihrer Struktur aufgeklärt, wobei die Struktur der einzelnen komplexen Ionen anhand von Schwingungsspektroskopie (Infrarot-, Ramanspektroskopie) ebenfalls bestätigt werden konnte. Mit Hilfe verschiedener kombinierter Desorptionsanalysen war es möglich den Zersetzungspfad, insbesondere die Bildung instabiler Desorptionsprodukte, aufzuklären. So erfolgt die Zersetzung des Li-Al-Borhydrids über die Bildung von Lithiumborhydrid in der Festphase, das mittels in-situ Ramanspektroskopie in einer speziellen Ramanzelle beobachtet werden konnte. Die Infrarotspektroskopie des Desorptionsgases zeigte zunächst die Freisetzung von Aluminiumborhydrid, dass wiederrum Diboran und Wasserstoff desorbiert. Weiterhin wurden verschiedene Möglichkeiten verfolgt, wie der Zusatz von Kohlenstoff oder das Nanoconfinement von Lithiumalanat, um den Zersetzungsweg hinsichtlich ausschließlicher Wasserstofffreisetzung zu modifizieren und somit Reversibilität zu ermöglichen. Es konnte jedoch kein reversibles System mit hoher gravimetrischer Wasserstoffspeicherdichte und Desorption unterhalb von 100°C erzeugt werden.Aim of the work was the synthesis and characterisation of novel mixed tetrahydroborates (borohydrides) for solid state hydrogen storage suitable for mobile applications. The combination with a PEM fuel cell requires a material with at least 6 wt% hydrogen combined with hydrogen desorption below 100°C. To fulfill both criteria, Li-Al- und Na-Al-borohydride were selected according to Nakamori’s concept. Both mixed borohydrides desorb well below 100°C whereas the mixed Li-Al-borohydride showed the most promising properties due to its high gravimetric hydrogen content (17.2 wt% H2). The crystal structures were examined by powder diffraction with a synchrotron source. The symmetry of the containing complex cations and anions was confirmed with vibrational spectroscopy (infrared, raman spectroscopy). The desorption pathway was clarified using a variety of combined thermal analysis techniques. Especially the desorption of unstable products of the most promising Li-Al-borohydride was possible via spectroscopy. Hence the desorption of Li-Al-borohydride leads to the formation of lithium borohydride in the solid state which was monitored via in-situ raman spectroscopy in a special raman cell. Infrared spectroscopy of the desorbed gas showed the initial desorption of aluminium borohydride which desorbs diborane and hydrogen in the following. Different options were examined in order to modify this desorption pathway by carbon addition or nanoconfinement of lithium alanate. However, none of the materials showed high hydrogen content combined with exclusive hydrogen desorption below 100°C and reversibility

Calciothermic Synthesis of Very Fine, Hydrogenated Ti and Ti–Nb Powder for Biomedical Applications

Due to their excellent biocompatibility, titanium and titanium–niobium alloys are especially interesting for biomedical applications. With regard to favorable near-net shape production, Ti powder synthesis is the key hurdle. Extensive research has been in progress for alternative synthesis methods since decades. Herein, an efficient alternative method to the conventional powder production process to prepare spherical powders with very small sizes (<45 μm) for high-strength materials is shown. Very fine, hydrogenated Ti and Ti–Nb alloy powders are stable in air and are synthesized by calciothermic reduction in hydrogen. The herein presented reduction using CaH2 starts directly from the oxides instead of chlorides. Correlations of size and morphology of the as-synthesized TiH2 and (Ti,Nb)H2 powders with the precursors (TiO2, Nb2O5, and CaH2) are illustrated and are used to tailor the desired powders

Insight into the decomposition pathway of the complex hydride Al3Li4(BH4)(13)

The decomposition pathway of the complex hydride Al3Li 4(BH4)13 is in the focus of this study. Initially the compound attracted great interest due to its high H2 capacity (17.2 wt.%) and desorption at moderate temperatures (&lt;100 °C). This work sheds light on its decomposition reaction by a unique experimental setup of thermogravimetry combined with spectroscopic gas phase analysis (FT-IR and MS) at ambient conditions. It is observed that the compound itself is metastable and decomposes immediately into its components, solid LiBH 4 and Al(BH4)3 which is monitored in the gas phase. Carbon addition decreases the observed mass loss and the spectroscopic gas phase analysis is used to learn about the impact of carbon addition. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Novel sodium aluminium borohydride containing the complex anion [Al(BH(4),Cl)(4)](-)

The synthesis of a novel alkali-metal aluminium borohydride NaAl(BH(4))xCl(4-x) from NaBH(4) and AlCl(3) using a solid state metathesis reaction is described. Structure determination was carried out using synchrotron powder diffraction data and vibrational spectroscopy. An orthorhombic structure (space group Pmn2(1)) is formed which contains Na(+) cations and complex [Al(BH(4),Cl)(4)](-) anions. Due to the high chlorine content (1 <= x <= 1.43) the hydrogen density of the borohydride is only between 2.3 and 3.5 wt.% H(2) in contrast to the expected 14.6 wt.% for chlorine free NaAl(BH(4))(4). The decomposition of NaAl(BH(4))(x)Cl(4-x) is observed in the target range for desorption at about 90 degrees C by differential scanning calorimetry (DSC), in situ Raman spectroscopy and synchrotron powder X-ray diffraction. Thermogravimetric analysis (TG) shows extensive mass loss indicating the loss of H(2) and B(2)H(6) at about 90 degrees C followed by extensive weight loss in the form of chloride evaporation

NaAlH4 confined in ordered mesoporous carbon

In this paper we performed a comprehensive investigation of the structural and sorption properties of a 40 wt. % NaAlH4 confined in a ordered mesoporous carbon (OMC, i.e. CMK-3) by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), 23Na{1H} and 27Al{1H} solid-state magic angle spinning-nuclear magnetic resonance (MAS-NMR). This study evidences a remarkable improvement of the sorption kinetics of NaAlH4 due to its existence in nanometer size within the OMC. The pressure composition isotherm (PCI) analysis (for the re-absorption step) of the nanoconfined NaAlH4 would suggest an alteration of its equilibrium thermodynamic properties

Al3Li4(BH4)13: A Complex Double-Cation Borohydride with a New Structure

The new double-cation Al-Li-borohydride is an attractive candidate material for hydrogen storage due to a very low hydrogen desorption temperature (~70 °C) combined with a high hydrogen density (17.2 wt %). It was synthesised by high-energy ball milling of AlCl3 and LiBH4. The structure of the compound was determined from image-plate synchrotron powder diffraction supported by DFT calculations. The material shows a unique 3D framework structure within the borohydrides (space group=P-43n, a=11.3640(3) Å). The unexpected composition Al3Li4(BH4)13 can be rationalized on the basis of a complex cation [(BH4)Li4]3+ and a complex anion [Al(BH4)4]-. The refinements from synchrotron powder diffraction of different samples revealed the presence of limited amounts of chloride ions replacing the borohydride on one site. In situ Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal desorption measurements were used to study the decomposition pathway of the compound. Al-Li-borohydride decomposes at ~70 °C, forming LiBH4. The high mass loss of about 20 % during the decomposition indicates the release of not only hydrogen but also diborane

Unusual oxidation behavior of light metal hydride by tetrahydrofuran solvent molecules confined in ordered mesoporous carbon

Confining light metal hydrides in micro- or mesoporous scaffolds is considered to be a promising way to overcome the existing challenges for these materials, e.g. their application in hydrogen storage. Different techniques exist which allow us to homogeneously fill pores of a host matrix with the respective hydride, thus yielding well defined composite materials. For this report, the ordered mesoporous carbon CMK-3 was taken as a support for LiAlH4 realized by a solution impregnation method to improve the hydrogen desorption behavior of LiAlH4 by nanoconfinement effects. It is shown that upon heating, LiAlH4 is unusually oxidized by coordinated tetrahydrofuran solvent molecules. The important result of the herein described work is the finding of a final composite containing nanoscale aluminum oxide inside the pores of the CMK-3 carbon host instead of a metal or alloy. This newly observed unusual oxidation behavior has major implications when applying these compounds for the targeted synthesis of homogeneous metal–carbon composite materials